Sensors and transducers are widely used in systems for data acquisition where physical properties are subject to be measured, gathered or analyzed. Measurements and gatherings of properties can be used for immediate use or for statistical purpose and analysis and can even further be used for monitoring or evaluation purposes.
In order to be able to make use of sensed signals, some kind of conditioning of the signal itself might be applicable. A sensor is hereby understood to be the sensing element and a transducer is often referred to as the sensing element together with means for conditioning and transmitting the sensed signal in a usable manner like a preamplifier circuit, and in the present context this is the meaning of the term transducer.
Sensors in this kind of areas can be based on several different elements and principles such as piezo-electric, piezo-resistive, capacitive or magneto restrictive.
For use in instrumentation and other areas, it is often of outmost importance that systems comprising sensors, transducers and related equipment can be field-tested in order to be highly reliable for gathering of trustworthy information. Several attempts have been made to accomplish this.
In WO 95/06259 and U.S. Pat. No. 5,753,793 there is disclosed a system where a piezo-electric transducer is exited from a generator and the resulting ringing of the transducer is analyzed. This straightforward approach can work for systems where the sensing device can be put in an oscillating state, but characterisation of the transducer system is not complete and the control systems necessary for the application need to be installed separately.
In WO 86/04137 there is disclosed a system comprising a primary and a secondary transducer which are built together. The secondary piezo-electric transducer can be energized by an introduced electrical signal and generates hereby a mechanical excitation to be picked up by the primary piezo-electric transducer. The difference signal is the signal measured and in case of no signal or faulty signal, the transducer is susceptible. This system will need considerably more special hardware and twice the cabling of a conventional circuit.
U.S. Pat. No. 6,698,269 discloses a system for test of transducers by means of a built-in test signal generator connected to the sensor-amplifier connection point for test and disconnecting the amplifier for analysis of the transducer. This system is based on the idea of exiting the sensor element by means of a generator generating a suitable electrical signal. The preamplifier in situ is not under test, and implementation and control of the system is an issue that remains to be solved.
U.S. Pat. No. 5,400,297 discloses a method and a system for injection of a test signal through a relatively small capacitor into the junction point of the inlet of a preamplifier for acoustic devices and a sensor. The system, which primarily is designed for capacitive voltage sensors, though adaptable for charge type sensors, requires a separate connection point with very high quality cabling in addition to the normal signal cabling.